Table of Contents

Passive House – the next decade

Focus – basis of efficiency criteria

Major changes in the energy supply structure over the next few years will lead to constantly changing primary energy factors. For that reason alone, the frequently used nonrenewable primary energy demand will no longer be suitable for assessing buildings' energy efficiency.

In order to determine a new measurement of efficiency that will serve its purpose for a longer time, this investigation is based on the following:

1. A complete transition to renewable energy supply is assumed (could occur by 2060). Buildings constructed or renovated today will use this supply structure for the majority of their lifecyles.

2. The use of renewable energy sources that will be sustainably available for the long term – photovoltaics, wind energy, hydropower, and sustainable biomass (waste) – is assumed. These technologies are already developed and available and are especially well suited to creating a completely sustainable energy supply [Welter 2012], as the present study confirms. This type of energy generation has become increasingly affordable and will be available at very reasonable prices by 2020. At least initially, however, energy costs will not drop below today's (2013).1)

3. Differences between renewables and conventional energy systems include the following:

The amount of renewable energy available at a given moment depends on meteorological conditions. Output fluctuates greatly and can even drop to almost zero. A renewable energy system must therefore include an adequate energy storage structure.

Renewables have a low power density and therefore require larger areas to generate enough energy. Space requirements are renewable energy's main resource problem.

To solve the first issue in point 3 (production dependent on weather), a two-step storage concept is recommended:

A short and mid-term grid storage structure consisting of conventional storage devices throughout the grid with low conversion losses (2 to 35 percent) and more than 60 storage cycles per year. Some options include pumped storage plants, other mechanical storage systems, and batteries. The applications themselves also have storage capacities, like hot water tanks and heat capacity in buildings (a temperature difference of 1 K is considered acceptable and results in storage losses of about ten percent). A quick calculation shows that all of these systems are far from suitable for long-term storage (less than five cycles per year), even if costs drop significantly (see [Feist 2013b]).

Seasonal / long-term storage. Exergetic storage systems are not available because of high costs and low energy density. Instead, converting energy into easily stored fuels is a good solution – for example, water electrolysis and hydrogen production, potentially as intermediate storage (conversion utilisation rate of up to 63 percent), or conversion into synthetic methane (3 H2 + CO2 → CH4 + 2 H2O), also called P2G (conversion efficiency rate of up to 57 percent) [Nitsch 2012], [Welter 2012]. The methane is stored in subsoil storage tanks with almost no losses, resulting in an expenditure factor of 1.75 kWh/kWh for private use of renewable methane. In an optimal situation, a 53-percent reconversion utilisation rate in a combined-cycle power plant can lead to an overall utilisation rate of about 33 percent; once the conversion sector's own consumption and distribution losses are included, the overall utilisation rate of seasonal storage for private users' electricity amounts to about 30 percent. Conversion losses create a greater demand for primary electricity, which must be generated from renewable sources. The increase in demands becomes greater as the seasonal correlation between energy applications' power demand and the primary generation structure worsens, in turn increasing the amount of space required for renewable energy generators (see Section Methodology).

The second issue in point 3 (low power density) results from the resources – in this case, the amount of space – that renewable structures require. These resource requirements are fundamentally different from those of fossil energy, where resource consumption is irreversible (hydrocarbon consumed) and product disposal leads to permanent pollution (CO2 in the atmosphere causes climate change; in the water, acidification). Renewables' resource requirements, on the other hand, are of a more aesthetic nature, with turbines easily seen throughout the landscape and PV arrays taking up large areas. It is important that PV arrays be installed on spaces already being used in some way, such as building roofs, façades, traffic routes and their boundary areas, etc. One problem related to space issues is of a social/economic nature. Land is already the most expensive natural resource, largely because there is already quite a bit of competition for using it and because it will be considered even more valuable in the future as the global population continues to grow – along with resource requirements. One way to measure the utilisation rate of renewable resources is by looking at overall primary electricity required (in kWh, power from wind, hydro, and PV systems). In this paper, this value will be referred to as renewable primary energy, or PER. PER is an ideal standard for assessing a structure's sustainability. To get an even clearer idea, PER can also be converted (with a generalized method) into regionally required equivalent PV generation area; at this time, an overall PV utilisation rate of ten percent (including line and conversion losses, shading, and dirty areas) can be assumed. An average of 1,000 kWh/m² of global insolation can be used for central Europe, which means that each 1 MWh requires an equivalent PV generation area of about 10 m².

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Consequences and outlook

Previous studies have shown that technology available today can be used in a highly efficient, completely renewable, and technically and economically reasonable regional energy supply, even in Central Europe. The transition will take a few years, since it must occur within the context of existing replacement and renovation cycles; otherwise, costs would be too high.

Parameter studies already conducted at various sites throughout Central Europe show that PER factors for the same applications differ only slightly. The differences are not much bigger for other sites in Europe (and even worldwide, except in the tropics). Based on the existing climate zone study ([Schnieders et al., 2012], see also [IPHT 2012]), PHI is cur­rently conducting a global study in order to determine the PER factors for all the PHPP climate datasets. Although the PER factors are quite similar, the average PV area needed to generate 1 MWh differs greatly from one location to the next, coming out to 10 m² in most of Germany, just 6.5 m² in Rom, 5.5 m² in San Francisco, and a mere 4.3 m² in the middle of the Sahara – but as much as 12 m² in Kiruna (Sweden) and Murmansk (Russia). All of these equivalent solar area figures are still within a range that is technically and eco­nomically feasible, meaning that (without consideration of regional availability of other primary renewable energy resources) PV can be used to supply Passive House buildings around the world. The necessary storage capacity and PER factors can be further decreased in the case of an interregional energy grid. The best solution here are high-voltage, direct-current transmission lines, since primary power generated in different locations could then come together on the grid. These kinds of solutions require a desire for fair international collaboration and would lead to better energy prices (especially in the winter), although they are not likely to go below the current price level in the foreseeable future.

Especially in light of a completely renewable energy supply in the future, the simulations run so far show that:

optimizing the building envelope and ventilation system efficiency beforehand is helpful. The functional (comfort and economic) criteria for Passive House are a very good starting point for a completely renewable worldwide energy supply. Applications that fluctuate greatly from season to season, like heating (or cooling, in regions that get hot in the summer), require additional grid, conversion, and storage systems and a much faster increase in primary power generators, resulting in higher energy prices. The Passive House Standard can contribute to keeping costs and complexity reasonable.

heat pump systems that run on electricity from the public grid have the highest overall efficiency, as long as useful heating demand remains in the Passive House range.

summertime cooling is no longer an energy application that must be avoided at all costs. As long as useful cooling demand also remains in the Passive House range, cooling demand can be easily covered as part of a renewable energy concept, especially if PV systems are installed.

See also

The current (mostly political) discussion about the supposedly “excessively high costs” of the energy transition are based on a number of incorrect conditions. However, the belief that energy will be “extremely cheap in the future” also lacks a realistic basis. Efficient systems are already a financially attractive alternative to today's mostly fossil-based supply (see [AkkP 42] and [Feist 2014a].